1, to prevent the destruction of membrane performance. New reverse osmosis membrane elements are usually immersed in 1% NaHSO3 and 18% glycerol aqueous solution and stored in sealed plastic bags. If the plastic bag is not broken, it will be stored for about 1 year, and its life and performance will not be affected. After the plastic bag is opened, it should be used as soon as possible to avoid adverse effects on the components due to the oxidation of NaHSO3 in the air. Therefore, the membrane should be opened as much as possible before use. After debugging the equipment, we used two methods to protect the film. The equipment is debugged for two days (15 ~ 24h), and then maintained with 2% formaldehyde solution; Or after running for 2 ~ 6h, use 1% NaHSO3 aqueous solution for maintenance (the air in the equipment pipeline should be exhausted to ensure that the equipment does not leak, and all import and export valves should be closed). Both methods can get satisfactory results. The first method is expensive and is used when the idle time is long, and the second method is used when the idle time is short.
2. Improper equipment operation will damage the performance of the membrane. There is residual gas in the equipment running under high pressure, and the air hammer will damage the membrane. There are two situations: a. After the equipment is evacuated, the gas will quickly increase in pressure when it is re-operated. The remaining air should be discharged at a pressure of 2 ~ 4 bar, and then gradually boosted. B. When the joint between the pretreatment equipment and the high-pressure pump is poorly sealed or leaked (especially when the microfilter and the pipeline behind it leak), when the pretreatment water supply is insufficient, such as the microfiltration is blocked, some air will be sucked in at the poorly sealed part due to vacuum. The microfilter should be cleaned or replaced to ensure that the pipeline does not leak. In short, the pressure should be gradually increased when there are no bubbles in the flowmeter, and gradually decreased when bubbles are found during operation, and the reasons should be checked. Incorrect method during shutdown A. Rapid depressurization during shutdown without thorough flushing. Because the concentration of inorganic salts on the concentrated water side of the membrane is higher than that of raw water, it is easy to scale and pollute the membrane. B, rinse with pretreatment water with chemical reagent. Because water containing chemical reagents may cause membrane pollution when the equipment is shut down. When preparing to stop, stop adding chemical reagents, gradually reduce the pressure to about 3bar, and rinse with pretreated water for 65438±00min until the TDS of concentrated water is very close to that of raw water.
3. Poor disinfection and maintenance lead to microbial pollution. This is a common problem in the use of polyamide composite membrane. Due to the poor residual chlorine resistance of polyamide membrane, improper addition of chlorine and other disinfectants during use, users pay insufficient attention to microbial prevention, which is easy to cause microbial pollution. At present, the microorganisms in purified water produced by many manufacturers exceed the standard, which are all caused by poor disinfection and maintenance. The main manifestations are as follows: RO equipment was not maintained with disinfectant when leaving the factory; After the installation of the equipment, the whole pipeline and pretreatment equipment were not disinfected; Disinfection and maintenance measures were not taken during intermittent operation; Disinfect pretreatment equipment and reverse osmosis equipment on a regular basis; Maintenance solution is invalid or the concentration is not enough. Poor monitoring of residual chlorine, such as pump failure or liquid medicine failure, or membrane damage caused by residual chlorine when activated carbon is saturated.
4. Damage to membrane performance caused by untimely cleaning and incorrect cleaning methods. In the process of equipment use, in addition to normal performance attenuation, equipment performance attenuation caused by pollution is more serious. The usual pollution mainly includes chemical scale, organic matter and colloid pollution, microbial pollution and so on. Different pollution shows different symptoms. Different membrane companies have different symptoms of membrane pollution. In the project, we found that the symptoms are different with different pollution time. If the membrane is polluted by calcium carbonate scale for a week, the desalination rate will decrease rapidly and the pressure difference will increase slowly, but the water yield will not change obviously. Washing with citric acid can completely restore the performance. After one year of pollution (one water purifier), the salt flux increased from the initial 2mg/L to 37mg/L (raw water was 140 mg/L ~ 160 mg/L), and the water yield decreased from 230L/h to 50 l/h. After washing with citric acid, the salt flux decreased to 7 mg/L. Moreover, pollution is often not single, and its symptoms are different, which increases the difficulty of identifying pollution. The identification of pollution types should be combined with raw water quality, design parameters, pollution index, operation records, equipment performance changes and microbial indicators: (1) Colloidal pollution: Colloidal pollution is usually accompanied by the following two characteristics: a. The microfilter is blocked quickly in pretreatment, especially the pressure difference increases rapidly, and the values of B and SDI are usually above 2.5. (2) Microbial contamination: When microbial contamination occurs, the total number of bacteria in the permeate water and concentrated water of RO equipment is high, so it must not be maintained and disinfected as required. (3) Calcium scale: It can be judged according to raw water quality and design parameters. For carbonate water, if the recovery rate is 75%, scale inhibitor is added in the design, and the LSI of concentrated solution should be less than1; Without scale inhibitor, the LSI of concentrated solution should be less than zero, and generally calcium scale will not be produced. (4) Insert 1/4 inch PVC plastic pipe into the assembly, and the performance changes of different parts of the assembly can be judged. (5) Determine the pollution type according to the change of equipment performance. (6) Acid washing (such as citric acid and dilute HNO3) can judge calcium scale according to the cleaning effect and cleaning solution, which is further confirmed by the composition analysis of cleaning solution. (7) Chemical analysis of cleaning solution: take raw water, cleaning stock solution and cleaning solution and analyze three samples. After determining the pollution type, it can be cleaned according to the method in table 1, and then disinfected for use. When the pollution type cannot be determined, the steps of cleaning (3)+ disinfection +0. 1%HCl(pH 3) are usually adopted. The steps of cleaning solution (1)+ cleaning solution (3)+ disinfection are also effective.